1. Field of the Invention
The present invention relates to an apparatus and method for recovering a disconnected communication link in a mobile communication system, and more particularly to an apparatus and method for reducing the overhead of resynchronization for a reconnection to a communication link which was disconnected during communication with a base station system in a mobile communication system.
2. Description of the Related Art
Unlike a wired link, a wireless channel between a Mobile Station (MS) (also called a “mobile communication terminal”) and a base station in a mobile communication system is affected by many external environmental factors. For example, while in motion, an MS connected to a base station through a wireless channel can enter a radio dead zone in which radio waves cannot reach, or enter the service area of another base station which is outside the service area of the first base station. As the MS moves from the service area of one base station to the service area of another base station, a wireless channel established with the MS is often abnormally disconnected (which terminates a communication service in progress) due to various factors, such as, failure to hand-off the communication service in progress from one wireless channel of one base station to another wireless channel of another base station.
FIG. 1 is a flow diagram showing a conventional method for recovering a communication link that is disconnected while an MS 100 is in communication with a Base Station System (BSS) 102 in a general mobile communication system. Here, it is assumed that a communication link, composed of a wireless channel SCHI, is established between the MS 100 and the BSS 102 (as shown in step 110). If a synchronization failure event occurs (i.e., if the communication link is disconnected) at step 112 (while the MS 100 is in communication with the BSS 102 at step 110), the MS 100 releases all resources for communication with the BSS 102 at step 114. Thereafter, the MS 100 attempts to reestablish a communication link with the BSS 102. Upon detecting that the communication link has disconnected, the BSS 102 performs a procedure for terminating all services in progress for communication with the MS 100 at step 116.
As described above, if the communication link with the MS 100 is disconnected, the BSS 102 generally terminates all services in progress for the communication with the MS 100, and the MS 100 attempts to reestablish a communication link with the BSS 102. If the MS 100 fails to reestablish a communication link with the BSS 102, the MS 100 must reestablish a communication link with a new BSS through handoff, and then reconnect to (or restart) services for communication with the new BSS.
When the MS 100 momentarily passes through a radio dead zone where it cannot receive services from the BSS 102, or when the MS 100 is located in a radio dead zone, or when the MS 100 is located in other compromised communication environments, the communication link between the MS 100 and the BSS 102 is frequently and repeatedly disconnected. Communication is then resumed between the MS 100 and the BSS 102 by establishing a new communication link. Thus, when a communication link is repeatedly disconnected and subsequently recovered, the MS 100 repeatedly connects to services and disconnects from services, which are provided through the BSS 102.
These frequently repeated link disconnections and recoveries, waste valuable time during which the MS 100 attempts to connect to the aborted services. Additionally, a large amount of data for the previous services (which was aborted), which has already been transmitted before the disconnection, must be discarded due to the abnormal termination of the previously established services. This is an inefficient process which wastes time, system resources and energy. Moreover, users are oftentimes inconvenienced by discontinuous transmissions and subsequent reconnection attempts using the conventional method.
In a mobile communication system where communication link disconnection and recovery frequently occurs, an MS and a base station terminate the service in progress each time the communication link is disconnected, and then restart the service through a communication link which is reestablished between the MS and the base station. Data which has been previously transmitted and temporarily stored for the aborted service is generally discarded in such a link reestablishment procedure. Even when an MS briefly passes through the radio dead zone and a communication link is subsequently lost, it takes a much longer time for the MS to reconnect to the service through a handoff to a new base station after releasing all resources for communication with the previous BSS. The reconnection process increases the load on both the MS and the BSS.